1. Field of the Invention
The invention pertains to a (cascaded) optical switch at least comprising one input path, a number of output paths, one or more (preferably two or more) switch or splitter stages each comprising one or more optical switches or splitters, and at least one gate for optically disconnecting at least one of the output paths from the input path.
2. Description of the Related Art
Such a cascaded optical switch is known from E. J. Murphy, "Enhanced performance switch arrays for optical switching networks," Proceedings 8th European Conference on Integrated Optics, Apr. 2-4, 1997, pp. EFD5-1/563-EFD5-4/566. FIG. 3b of this publication shows a strictly non-blocking 4.times.4 switch matrix comprising, in its input stage, four 1.times.4 cascaded switches each consisting of an input path, a first stage consisting of a passive 3 dB splitter, a second stage consisting of two "dump" or signal disconnect switches, a third stage consisting of two 1.times.2 switches, and four output paths.
The dump switch stage makes it possible for any or all of the signal paths to be optically disconnected from the network of which they are a part. Disconnection of all signals may be necessary, for instance, during rearrangement of the 4.times.4 switch matrix or for diagnostics.
FIG. 1 of WO 96/08932 shows a tree-structured (i.e., cascaded) 1.times.8 optical switch wherein each output path is allocated a gate for selectively blocking and unblocking said output as a function of the state of the 1.times.2 switch nearest to the output. Disconnection of all the outputs from the input, as required during the above-described rearrangement, can be achieved by activating all eight gates so as to block all outputs.
Another example of a cascaded switch is shown in FIG. 1 accompanying this patent application. This cascaded switch comprises one input path (4), a first switch stage (1) consisting of one thermo-optical 1.times.2 switch (viz. a y-junction switch provided with two heater elements), a second switch stage (2) consisting of two thermo-optical 1.times.2 switches (the first and second stages forming a 1.times.4 switch), a third stage (3) consisting of four gates (6; in this case thermo-optical 2.times.1 switches), and four output paths (5/5'). Again, optical disconnection of all the outputs from the input can only be achieved by activating all four gates so as to block all outputs.